306 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
(Partial resorption followed regeneration) was measured and likewise 
the area between the two curves. The latter was expressed as a 
per cent of the former. The result is a quantitative expression of 
retardation (or acceleration) of regeneration which can be compared 
with similar quantities for other experiments, whereby are avoided 
such errors as would arise from differences between the degree of 
regeneration of the control in different experiments. 
Acceleration and retardation were found to result from different 
types of exposure, as seen in Figs. 5 and 6. The conditions determin- 
ing whether acceleration or retardation will occur are shown by the 
correlation tables (Figs. 7 and 8), which include the results of all 
experiments. ‘The ordinates indicate the number of hours of exposure 
ee a eo ae Can? eres | 
Fig. 7.— Correlation table showing the relation between length of exposure and 
per cent of retardation. 
The units of the ordinate indicate the hours of exposure. 
The units of the abscissa indicate per cent of development. 
The numbers in parentheses indicate relative development before beginning of 
exposure. 
to radium. The abscissas in Fig. 7 stand for per cent retardation, 
and in the next table, for per cent acceleration calculated from the 
areas of the curves. The dots in Fig. 7 and the circles of Fig. 8 stand 
each for an experiment. The connecting of a dot to a circle is to show 
that acceleration and retardation occurred at different times in the 
same experiment. 
The chief cause of the acceleration shown in Fig. 8 is apparent 
upon comparing the lengths of treatment in it with those which pro- 
